Alternate Version of STARTING OUT WITH C 4th Edition

1
Alternate Version of STARTING OUT WITH C 4th
Edition

• Chapter 3
• Expressions and Interactivity

2
The cin Object

• Standard input object
• Like cout, requires iostream file
• Used to read input from keyboard
• Often used with cout to display a user prompt
  first
• Data is retrieved from cin with gtgt
• Input data is stored in one or more variables

3
The cin Object

• User input goes from keyboard to the input
  buffer, where it is stored as characters
• cin converts the data to the type that matches
  the variable
• int height
• cout ltlt "How tall is the room? "
• cin gtgt height

4
The cin Object

• Can be used to input multiple values
• cin gtgt height gtgt width
• Multiple values from keyboard must be separated
  by spaces or Enter
• Order is important first value entered is stored
  in first variable, etc.

5
Mathematical Expressions

• An expression can be a constant, a variable, or a
  combination of constants and variables combined
  with operators
• Can create complex expressions using multiple
  mathematical operators
• Example mathematical expressions
• 2
• height
• a b / c

6
Using Mathematical Expressions

• Can be used in assignment statements, with cout,
  and in other types of statements
• Examples
• area 2 PI radius
• cout ltlt "border is " ltlt 2(lw)

7
Order of Operations

• In an expression with gt 1 operator, evaluate in
  this order
• - (unary negation) in order, left to right
• / in order, left to right
• - in order, left to right
• In the expression 2 2 2 2 ,

Do first
Do next
Do last
8
Associativity of Operators

• - (unary negation) associates right to left
• / - all associate left to right
• parentheses ( ) can be used to override the order
  of operations
• 2 2 2 2 4
• (2 2) 2 2 6
• 2 2 (2 2) 2
• (2 2) (2 2) 0

9
Algebraic Expressions

• Multiplication requires an operator
• Area lw is written as Area l w
• There is no exponentiation operator
• Area s2 is written as Area pow(s, 2)
• Parentheses may be needed to maintain order of
  operations
• is written as
• m (y2-y1)/(x2-x1)

10
Implicit Type Conversion

• Operations are performed between operands of the
  same type
• If not of the same type, C will automatically
  convert one to be the type of the other
• This can impact the results of calculations

11
Hierarchy of Data Types

• Highest
• Lowest
• Ranked by largest number they can hold

long double double float unsigned
long long unsigned int int
12
Type Coercion

• Coercion automatic conversion of an operand to
  another data type
• Promotion converts to a higher type
• Demotion converts to a lower type

13
Coercion Rules

• 1) char, short, unsigned short are automatically
  promoted to int
• When operating on values of different data types,
  the lower one is promoted to the type of the
  higher one.
• When using the operator, the type of
• expression on right will be converted to
  type of variable on left

14
Explicit Type Conversion

• Also called type casting
• Used for manual data type conversion
• Format
• static_castlttypegt(expression)
• Example
• cout ltlt static_castltchargt(65)
• // Displays A

15
More Type Casting Examples

• char ch 'C'
• cout ltlt ch ltlt " is stored as "
• ltlt static_castltintgt(ch)
• cartons static_castltintgt(eggs/12)
• avg static_castltfloatgt(sum)/count

16
Overflow and Underflow

• Occurs when assigning a value that is too large
  (overflow) or too small (underflow) to be held in
  a variable
• Variable contains value that is wrapped around
  the set of possible values

17
Overflow Example

• // Create a short int initialized to
• // the largest value it can hold
• short int num 32767
• cout ltlt num // Displays 32767
• num
• cout ltlt num // Displays -32768

18
Handling Overflow and Underflow

• Different systems handle the problem differently.
  They may
• display a warning / error message
• stop the program
• or just continue execution

19
Named Constants

• Also called constant variables
• Variables whose content cannot be changed during
  program execution
• Used for representing constant values with
  descriptive names
• const float TAXRATE 0.0675
• const int NUMSTATES 50
• Often named in uppercase letters

20
const vs. define

• define
• C-style of naming constants
• define NUMSTATES 50
• Interpreted by pre-processor rather than compiler
• Does not occupy a memory location like a constant
  variable defined with const
• Instead, causes a textual substitution to occur.
  In above example, every occurrence in program of
  NUMSTATES will be replaced by 50

21
Multiple Assignment and Combined Assignment

• The assignment operator () can be used gt 1 time
  in an expression
• x y z 5
• Associates right to left
• x (y (z 5))

22
Combined Assignment

• Applies an arithmetic operation to a variable and
  assigns the result as the new value of that
  variable
• Operators - /
• Example
• sum amt is short for sum sum amt

23
More Examples

• x 5 means x x 5
• x - 5 means x x 5
• x 5 means x x 5
• x / 5 means x x / 5
• x 5 means x x 5
• The entire right hand side is evaluated before
  the
• combined assignment operation is done.
• x a b means x x (a b)

24
Formatting Output

• Can control how output displays for numeric and
  string data
• size
• position
• number of digits
• Requires iomanip header file

25
Stream Manipulators

• Used to control features of an output field
• Some affect just the next value displayed
• setw(x) Print in a field at least x spaces wide.
  Use more spaces if specified field width is not
  big enough.

26
Stream Manipulators

• Some affect values until changed again
• fixed Use decimal notation (not E-notation) for
  floating-point values.
• setprecision(x)
• When used with fixed, print floating-point value
  using x digits after the decimal.
• Without fixed, print floating-point value using x
  significant digits.
• showpoint Always print decimal for
  floating-point values.

27
Manipulator Examples

• const float e 2.718
• float price 25.0 Displays
  
  
• cout ltlt setw(8) ltlt e ltlt endl 2.718
• cout ltlt setprecision(2)
• cout ltlt e ltlt endl 2.7
• cout ltlt fixed ltlt e ltlt endl 2.72
• cout ltlt setw(6) ltlt price 18.00

28
Working with Characters and String Objects

• char holds a single character
• string holds a sequence of characters
• Both can be used in assignment statements
• Both can be displayed with cout and ltlt

29
Character Input

• Reading in a character
• char ch
• cin gtgt ch // Reads in any non-blank char
• cin.get(ch) // Reads in any char
• cin.ignore() // Skips over next char in
• // the input buffer

30
String Input

• Reading in a string object
• string str
• cin gtgt str // Reads in a string
• // with no
  blanks
• getline(cin, str) // Reads in a string
• // that
  may contain
• // blanks

31
String Operators

• Assigns a value to a string
• string words
• words Tasty
• Joins two strings together
• string s1 hot", s2 "dog"
• string food s1 s2 // food hotdog"
• Concatenates a string onto the end of another
  one
• words food // words now Tasty hot dog"

32
Using C-Strings

• C-string is stored as an array of characters
• Programmer must indicate maximum number of
  characters at definition
• char temp5 "Hot"
• NULL character (\0) is placed after final
  character to mark the end of the string
• Programmer must make sure array is big enough for
  desired use temp can hold up to 4 characters
  plus the \0.

33
C-String Input

• Reading in a C-string
• char Cstr10
• cin gtgt Cstr // Reads in a C-string with no
• // blanks. Will
  write past the
• // end of the
  array if input string
• // is too long.
• cin.getline(Cstr, 10)
• // Reads in a
  C-string that may
• // contain blanks.
  Ensures lt 9
• // chars are read
  in.

34
C-String Initialization vs. Assignment

• A C-string can be initialized at the time of its
  creation (just like a string object can)
• char month10 April
• However, a C-string cannot later be assigned a
  value using the operator you must use the
  strcpy() function
• char month
• month April // wrong!
• strcpy(month, April) //correct

35
More Mathematical Library Functions

• These require cmath header file
• Take double arguments and return a double
• Commonly used functions

abs Absolute value
sin Sine
cos Cosine
tan Tangent
sqrt Square root
log Natural (e) log
36
More Mathematical Library Functions

• These require cstdlib header file
• rand
• Returns a random number between 0 and the largest
  int the computer holds
• With the same seed, will yield same sequence of
  numbers each time program is run
• srand(x)
• Initializes random number generator with
• unsigned int x

37
Introduction to Files

• Can use a file instead of keyboard for program
  input
• Can use a file instead of monitor screen for
  program output
• Files are stored on secondary storage media, such
  as disk
• They allow data to be retained between program
  runs

38
What is Needed to Use Files

• Include the fstream header file
• Define a file stream object
• ifstream for input from a file
• ifstream infile
• ofstream for output to a file
• ofstream outfile

39
Open the File

• Open the file
• Use the open member function
• infile.open("inventory.dat")
• outfile.open("report.txt")
• Filename may include drive, path info.
• Output file will be created if necessary
  existing file will be erased first
• Input file must exist for open to work

40
Use the File

• Use the file
• Can use output file object and ltlt to send data to
  a file
• outfile ltlt "Inventory report"
• Can use input file object and gtgt to copy data
  from file to variables
• infile gtgt partNum
• infile gtgt qtyInStock gtgt qtyOnOrder

41
Close the File

• Close the file
• Use the close member function
• infile.close()
• outfile.close()
• Dont wait for operating system to close files at
  program end
• May be limit on number of open files
• May be buffered output data waiting to be sent to
  a file